1. Field of the Invention
This invention is directed to deep fat cooking equipment and particularly the temperature control system for controlling the temperature of the deep fat therein for proper deep fat cooking.
2. Description of the Prior Art
Prior art deep fat cooking equipment includes a vessel in which the deep fat is contained and heated. Food items are placed in this deep fat and are cooked therein at an appropriate temperature and for an appropriate time. A heater is submerged in the deep fat, and the heater is controlled to attempt to maintain proper cooking conditions in the deep fat.
There are three heating conditions in a deep fat cooking system which require the control of the heater. First, when the vessel and the fat therein are cool, the heat input rate may have to be reduced if the heater power is large. Second, the raising of the temperature from the cold to the desired cooking temperature should be accomplished smoothly without the heater turning off too soon and without the heater turning off too late. In the first case, the desired cooking temperature is not reached as quickly as is desired for proper cooking and, in the second case, overheating of the cooking oil reduces its life and may raise the oil temperature to a dangerously high value, as far as both proper cooking and fire are concerned.
Prior art deep fat fryers have a cooking vat with an electric heater submerged in the oil in the bottom of the vat. A temperature sensor in the form of a bulb on the end of a capillary tube is supported closely adjacent and under the heater element. That temperature sensor is in the hot zone so that it turns off too soon, because it measures the oil temperature very close to the heater and not in the cooking zone above the heater. In other cases, the sensor is positioned in a corner of the vat in order to protect it from damage from the food baskets, but when the sensor is in an out-of-the-way position, the heater is likely to stay on too long because the temperature sensor is too far away from the heater. Convection is poor, even in heated oil, because of the viscosity. Conduction is also poor so that, when the sensor is located in an out-of-the-way place, the oil around the heater and in the cooking zone get too hot before set temperature is sensed.
As far as heating up is concerned, one teaching states that, during the melting cycle, the intial melting occurs during reduced heat input from the electric heater, and when the temperature sensor in the vat reaches a certain temperature, then the heater goes into full heating power condition. However, this system is not satisfactory because, when a block of solid shortening is placed in the vat, the heater melts the bottom of the block up to fill the bottom of the vat around the heater and then the fat circulates up around the block of still solid shortening. This circulating liquid is in contact with the temperature sensor which signals that the full heating power should be applied. However, since there is solid shortening in the vat, circulation is inhibited, and local overheating is likely.
Furthermore, during the cooking cycle when food product is put into the hot oil to be cooked, there is a considerable demand for heat because a considerable amount of heat is extracted from the hot oil by the boiling off of water in the food product. In order to maintain the deep fat at the proper temperature, its temperature condition must be sensed. Therefore, there is need not only to sense the temperature directly adjacent the heater, but also need to sense the deep fat temperature in the cooking zone.